Display with an electrically conducting layer

ABSTRACT

A display for showing text and graphical images includes an electrically conducting layer which is connected to a shield potential, such as a ground potential, for shielding the display from external electromagnetic disturbances and preventing radiation from the display of electromagnetic disturbances generated by the display.

PRIORITY CLAIM

This is a U.S. national stage of application No. PCT/DE01/04811, filedon Dec. 20, 2001. Priority is claimed on that application and on thefollowing application: Country: Germany, Application No.: 100 64 921.1,Filed: Dec. 23, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a display for showing text and graphic imageswith an electrically conducting layer. Displays with an electricallyconducting layer. Displays with an electrically conducting layer areknown in the prior art and are used to make the display form a so-called“touch screen” or, for example in the case of liquid-crystal displays,to heat them. Heating devices are used in the case of liquid-crystaldisplays in order that they can operate quickly even at lowtemperatures, as may occur for example when they are used in motorvehicles, and in this way prevent a display with a slow response.

2. Description of the Prior Art

A “touch screen” is known in the prior art and is used to allow menus,submenus, values or icons represented on a screen to be selected bytouching the respective representation with a finger or some other inputmeans. In the case of an analog resistive touch screen, a plate oftoughened glass with an electrically conductive coating with a uniformelectrical resistance is arranged in front of the display. A sheet ofpolyester is stretched over this glass upper side and separated from itby small, transparent insulating points. The variable sheet has a hard,durable coating on the outer side and a conductive and highlytransparent indium-tin-oxide coating on the inside. Even when touchedlightly, the conductive coating establishes an electrical connectionwith the coating on the glass. By means of an integrated controller, avoltage gradient is set up on the conductive coating. The voltages atthe contact point form an image of the touched position with the aid ofanalog values. The controller digitizes these voltages and sends them toa processing device to determine the touched positions.

A capacitive touch screen comprises a clear plate which has been coatedwith a resistively capacitive material and an insulating material. Anelectromagnetic field is generated over the plate. If a conductingobject, for example a finger or metal rod, touches the screen andgrounds it, the electromagnetic field changes. The place which wastouched can be concluded from the change in the electromagnetic field.

Displays and the driver circuits controlling them are operated with highfrequencies. Consequently, undesired electromagnetic disturbances canoccur in the area surrounding the displays. If a display is used in aninstrument cluster of a motor vehicle, the radio reception and/or thecell phone reception in the motor vehicle for example may be disturbed.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to provide a display with anelectrically conducting layer which causes the least possibleelectromagnetic disturbances and does not allow electromagneticdisturbances caused by the drive electronics to pass through and whichis constructed in a simple and inexpensive way. This object is achievedaccording to the invention by the electrically conducting layer beingconnected to a shielding potential for high frequencies. The effect ofthis is that the electrically conducting layer is at the shieldingpotential for high frequencies and high frequencies are consequentlyprevented from passing through. The high-frequency connection may takeplace for example with capacitors which are arranged between theelectrically conducting layer and the shielding potential, one terminalof the capacitor being connected to the electrically conducting layerand one terminal being connected to the shielding potential. In cases inwhich a DC connection between the electrically conducting layer and theshielding potential is unproblematical, it is also possible to establishthe connection of the heating and the shielding potential by anelectrically conductive element.

The shielding potential may be realized for example by a metal housingor by a metallized housing, the housing being closed by the display.Under some circumstances, depending on the required shielding effect, itmay be adequate to connect the liquid-crystal display to a groundpotential by a high-frequency connection.

The electrically conducting layer may be made up of indium-tin oxide(ITO), which covers the display over its surface area.

If the display is formed as a liquid-crystal display, the electricallyconducting layer may be formed as a heating device, which is flowedthrough by a heating current. It is also possible to realize the heatingdevice by means of current-conducting paths, which are arrangedindividually or in a meandering form. If these paths run between theelectrodes of the liquid-crystal cells and consist of indium-tin oxide,they can be produced in one operation with the electrodes of theliquid-crystal cells.

It is also possible for the electrically conducting layer to be formedas part of a touch screen. In this case, the display may be formed forexample as a liquid-crystal display, OLED display or as a monitor. Ifthe display is formed as a liquid-crystal display, and an electricallyconducting layer of a touch screen is arranged in front of it, theelectrically conducting layer may also be used at the same time asheating for the liquid-crystal display.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote similarelements throughout the several views:

FIG. 1 is a partial sectional view of a liquid-crystal cell with heatingapplied over its surface area and the connection to a shieldingpotential;

FIG. 2 is an exploded view of a front and rear walls of a liquid-crystalcell;

FIG. 3 is a sectional view through a liquid-crystal cell and a shieldinghousing; and

FIG. 4 is an exploded view of a touch screen with a monitor.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

In FIG. 1, a liquid-crystal cell 1 has a front wall 2 a and a rear wall2 b. On the front wall 2 a and the rear wall 2 b, heating layers 3 a, 3b have been respectively applied over their surface area and arerespectively separated from front and rear electrodes 5 a, 5 b byinsulations 4 a, 4 b. The front and rear electrodes 5 a, 5 b are finallyseparated from a liquid-crystal substance 7 by insulations 6 a, 6 b. Thefront and rear heating layers 3 a, 3 b are connected to a groundpotential M via contact clips 8 a, 8 b, electrical conductors 9 a, 9 b,capacitors 10 a, 10 b. Consequently, high-frequency disturbancesimpinging on the heating layers 3 a, 3 b can be conducted via thecontact clips 8 a, 8 b electrical conductors 9 a, 9 b capacitors 10 a,10 b to the ground potential M.

An adhesive bond 11 connects the front wall 2 a to the rear wall 2 b andprevents any escape of the liquid-crystal substance 7.

The driving of the electrodes 5 a, 5 b for influencing theliquid-crystal substance 7 has long been known and is therefore notexplained any further here.

In FIG. 2, a front wall 12 a and a rear wall 12 b of anotherliquid-crystal cell 1 a can be seen. Arranged on the front wall 12 a areelectrodes 13 a and arranged on the rear wall 12 b are electrodes 13 b.Arranged between the electrodes 13 a of the front wall 12 a are heatingwires 14 a, which are connected to one another via contact pins 15 andconnections 16 a arranged on the rear wall 12 b and are consequentlyconnected in series. Arranged between the electrodes 13 b of the rearwall are heating wires 14 b, which are likewise connected via contactpins (not represented) and connections 16 b arranged on the front wall12 a and are consequently connected in series. The heating wires 14 a,14 b are connected via terminals 17 a, 17 b to a shielding potential(not represented). The arrangement of the heating wires 14 a, 14 b atright angles in relation to one another produces an arrangement of theheating wires 14 a, 14 b in the overall form of a grid, so that, with ahigh-frequency connection to a shielding potential, high frequencies areprevented from passing through a display which has the componentsrepresented in FIG 2.

FIG. 3 shows a liquid-crystal cell 1 with a heating (not represented),which may be configured in the same way as the heatings of theliquid-crystal cells 1, 1 a represented in FIG. 1 or 2. The heatingdevice is electrically connected to a shielding housing 20 via contactclips 8 a, 8 b and capacitors 10 a, 10 b. The shielding housing 20 maybe produced from metal or be coated with a metal. Consequently, theinterior of the shielding housing 20 is largely isolated for highfrequencies from the area surrounding the shielding housing. Nodisturbances can penetrate into the interior from outside. Similarly,disturbances which are caused by a driving circuit 21 also cannot getthrough to the outside and consequently disturb devices in the areasurrounding the liquid-crystal cell 1, 1 a.

In FIG 4, a monitor 27, a glass layer 22, transparent metal films 23,24, an electron raster 25 and a glass layer 26 can be seen. The metalfilms 23, 5 24 have been vapor-deposited on the glass layer 22. Theelectron raster 25 has been vapor-deposited in the edge region on themetal film 23. The glass layer 2G has been applied to protect the touchscreen. A low AC voltage is applied to the electron raster 25 at allfour corners.

If the surface of the screen is then touched by a finger, the potentialof the finger draws a tiny amount of charge from each corner point.Since the current flow from four corners of the touch screen isproportional to the distance between the corner and the point touched,the precise location at which the touch screen was touched can becalculated and consequently a menu or submenu represented in this regionof the monitor, or the displayed value or icon can be selected. Themetal film 24 is connected to the ground potential M via a capacitor 10.Consequently, high-frequency electromagnetic radiations of the monitoror of some other display present in place of the monitor 27 areshielded.

If a liquid-crystal display is used in place of the monitor 27, themetal film 24 may be used at the same time for heating theliquid-crystal display.

1. A display for showing text and graphical images, comprising: a liquidcrystal display having a display surface and means for displaying thetext and graphical images, said means comprising electrodes connected toa driving circuit; a terminal connected to a shielding potential; anelectrically conducting layer covering said display surface area, saidelectrically conducting layer being separate from said electrodes, and aconnection comprising a capacitance between said electrically conductinglayer and said terminal connected to a shielding potential, saidconnection connecting high frequency signals on said electricallyconducting layer to said shielding potential for at least one ofshielding said display from external electromagnetic disturbances andpreventing radiation from said display of electromagnetic disturbancesgenerated by said means for displaying.
 2. The display of claim 1,further comprising a capacitor providing said capacitance.
 3. Thedisplay of claim 1, wherein said terminal connected to said shieldingpotential is connected to one of a metal housing and a metallizedhousing enclosed by said display.
 4. The display of claim 1, whereinsaid shielding potential is a ground potential.
 5. The display of claim1, wherein said electrically conducting layer comprises indium-tinoxide.
 6. The display of claim 1, wherein said electrically conductinglayer comprises a heating device.
 7. The display of claim 6, whereinsaid electrically conducting layer comprises current-conducting pathsarranged on said liquid-crystal display.
 8. The display of claim 7,wherein said liquid-crystal display comprises electrodes and saidcurrent-conducting paths are arranged between said electrodes.
 9. Thedisplay of claim 7, wherein said currently conducting paths compriseindium-titanium oxide.
 10. The display of claim 1, further comprising atouch screen, wherein said electrically conducting layer comprises apart of said touch screen.
 11. The display of claim 10, wherein saidelectrically-conducting layer is also arranged for heating theliquid-crystal display.
 12. The display of claim 1, wherein said meansfor displaying comprises a driver circuit controlling said display andsaid high frequency signals connected to said shielding potential arecaused by said drive electronics, said connection preventingelectromagnetic disturbances caused by radiation of said high frequencysignals in an area surrounding said display.